Immunity against schistosomes both in natural human infections and in various experimental models appears to be based on an antibody-dependent eosinophil mediated process. The in vitro experimental evidence for this is substantial. However, compelling demonstration and proof that these cells are the primary effect (helminthotoxic) cells in vivo has not been forthcoming. The present proposal aims to elucidate and clarify the role of eosinophils in the expression of immunity in murine experimental models. Specifically, the participation of eosinophils in resistance in the chronic Schistosoma mansoni infection model and in the S. mansoni irradiated cercariae vaccine model will be elucidated by pertubation of these cells in vivo through the application of documented, eosinophil-specific monoclonal antibodies. Passive transfer of resistance by serum from each model system will be also used. Elimination of eosinophils in such normal recipients of immune serum will be effected by the eosinophil monoclonal antibodies and the resistance thus abrogated. The final aim of this proposal is to similarly document the contribution of eosinophils in the development of S. mansoni egg granulomas in the model of synchronous granuloma formation in the pulmonary microvasculature in mice given isolated eggs intravenously. The eosinophil monoclonal antibodies will be used to drastically reduce the rate of growth of these granulomas. This will prolong the viability of tissue laid eggs as eosinophils appear to be the cells that destroy the eggs in situ.